FFmpeg/libavcodec/cabac.h

/*
 * H.26L/H.264/AVC/JVT/14496-10/... encoder/decoder
 * Copyright (c) 2003 Michael Niedermayer <michaelni@gmx.at>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */
 
/**
 * @file cabac.h
 * Context Adaptive Binary Arithmetic Coder.
 */


#undef NDEBUG
#include <assert.h>

typedef struct CABACContext{
    int low;
    int range;
    int outstanding_count;
#ifdef STRICT_LIMITS
    int symCount;
#endif
    uint8_t lps_range[2*64][4];   ///< rangeTabLPS
    uint8_t lps_state[2*64];      ///< transIdxLPS
    uint8_t mps_state[2*64];      ///< transIdxMPS
    uint8_t *bytestream;
    int bits_left;                ///<
    PutBitContext pb;
}CABACContext;

const uint8_t ff_h264_lps_range[64][4];
const uint8_t ff_h264_mps_state[64];
const uint8_t ff_h264_lps_state[64];

void ff_init_cabac_encoder(CABACContext *c, uint8_t *buf, int buf_size);
void ff_init_cabac_decoder(CABACContext *c, uint8_t *buf, int buf_size);
void ff_init_cabac_states(CABACContext *c, uint8_t const (*lps_range)[4], 
                          uint8_t const *mps_state, uint8_t const *lps_state, int state_count);


static inline void put_cabac_bit(CABACContext *c, int b){
    put_bits(&c->pb, 1, b); 
    for(;c->outstanding_count; c->outstanding_count--){ 
        put_bits(&c->pb, 1, 1-b);
    }
}

static inline void renorm_cabac_encoder(CABACContext *c){
    while(c->range < 0x100){
        //FIXME optimize
        if(c->low<0x100){
            put_cabac_bit(c, 0);
        }else if(c->low<0x200){
            c->outstanding_count++;
            c->low -= 0x100;
        }else{
            put_cabac_bit(c, 1);
            c->low -= 0x200;
        }
        
        c->range+= c->range;
        c->low += c->low;
    }
}

static inline void put_cabac(CABACContext *c, uint8_t * const state, int bit){
    int RangeLPS= c->lps_range[*state][((c->range)>>6)&3];
    
    if(bit == ((*state)&1)){
        c->range -= RangeLPS;
        *state= c->mps_state[*state];
    }else{
        c->low += c->range - RangeLPS;
        c->range = RangeLPS;
        *state= c->lps_state[*state];
    }
    
    renorm_cabac_encoder(c);

#ifdef STRICT_LIMITS
    c->symCount++;
#endif
}

static inline void put_cabac_static(CABACContext *c, int RangeLPS, int bit){
    assert(c->range > RangeLPS);

    if(!bit){
        c->range -= RangeLPS;
    }else{
        c->low += c->range - RangeLPS;
        c->range = RangeLPS;
    }

    renorm_cabac_encoder(c);

#ifdef STRICT_LIMITS
    c->symCount++;
#endif
}

static inline void put_cabac_bypass(CABACContext *c, int bit){
    c->low += c->low;

    if(bit){
        c->low += c->range;
    }
//FIXME optimize
    if(c->low<0x200){
        put_cabac_bit(c, 0);
    }else if(c->low<0x400){
        c->outstanding_count++;
        c->low -= 0x200;
    }else{
        put_cabac_bit(c, 1);
        c->low -= 0x400;
    }
        
#ifdef STRICT_LIMITS
    c->symCount++;
#endif
}

static inline void put_cabac_terminate(CABACContext *c, int bit){
    c->range -= 2;

    if(!bit){
        renorm_cabac_encoder(c);
    }else{
        c->low += c->range;
        c->range= 2;
        
        renorm_cabac_encoder(c);

        assert(c->low <= 0x1FF);
        put_cabac_bit(c, c->low>>9);
        put_bits(&c->pb, 2, ((c->low>>7)&3)|1);
        
        flush_put_bits(&c->pb); //FIXME FIXME FIXME XXX wrong
    }
        
#ifdef STRICT_LIMITS
    c->symCount++;
#endif
}

static inline void renorm_cabac_decoder(CABACContext *c){
    while(c->range < 0x10000){
        c->range+= c->range;
        c->low+= c->low;
        if(--c->bits_left == 0){
            c->low+= *c->bytestream++;
            c->bits_left= 8;
        }
    }
}

static inline int get_cabac(CABACContext *c, uint8_t * const state){
    int RangeLPS= c->lps_range[*state][((c->range)>>14)&3]<<8;
    int bit;
    
    c->range -= RangeLPS;
    if(c->low < c->range){
        bit= (*state)&1;
        *state= c->mps_state[*state];
    }else{
        bit= ((*state)&1)^1;
        c->low -= c->range;
        c->range = RangeLPS;
        *state= c->lps_state[*state];
    }
    renorm_cabac_decoder(c);
    
    return bit;    
}

static inline int get_cabac_static(CABACContext *c, int RangeLPS){
    int bit;
    
    c->range -= RangeLPS;
    if(c->low < c->range){
        bit= 0;
    }else{
        bit= 1;
        c->low -= c->range;
        c->range = RangeLPS;
    }
    renorm_cabac_decoder(c);
    
    return bit;    
}

static inline int get_cabac_bypass(CABACContext *c){
    c->low += c->low;

    if(--c->bits_left == 0){
        c->low+= *c->bytestream++;
        c->bits_left= 8;
    }
    
    if(c->low < c->range){
        return 0;
    }else{
        c->low -= c->range;
        return 1;
    }
}

static inline int get_cabac_terminate(CABACContext *c){
    c->range -= 2<<8;
    if(c->low < c->range){
        renorm_cabac_decoder(c);    
        return 0;
    }else{
        return 1;
    }    
}